I like to say Kirk is faking it because Kirk wouldn't necessarily be a very good actor. Thus the line delivery is less hilarious. However, if that is righteous anger, it's kind of comes off as way over the top. I'm a huge Shatner fan, but felt more like a TJ Hooker moment than a Kirk bit.
Just an aside, here:
Am I the only one who noticed Kirstie Alley mouthing The Shat's lines on the bridge, before she stands up and delivers her "General Order 12" remark?
I give her credit for knowing her cue lines, but if you gotta do that, you're just not in the moment, ya know?